1. Field of the Invention
The present invention relates to a sensor and a method of detecting a fingerprint capable of differentiating a forged fingerprint by detecting blood streams within an object in contact therewith using overlapping ultrasonic signals in a region in which the ultrasonic signals emitted through a plurality of piezoelectric sensors have relatively high intensity due to the overlap thereof.
2. Description of the Related Art
A fingerprint detection sensor, a sensor for detecting a human fingerprint, has been used in apparatuses such as an existing door lock, or the like, and has also been widely used to determine whether a power supply of an electronic device is turned on or off or whether a sleep mode thereof has been released. In particular, unlike the type of fingerprint detection sensor generally used for the door lock, a swipe type finger detection sensor capable of being configured to have a small volume has recently been developed, and thus, the fingerprint detection sensor is prevalently being used in mobile devices.
Fingerprint detection sensors may be classified into an ultrasonic type, an infrared type, a capacitive type, or the like, according to an operational principle thereof. Among these, the ultrasonic type fingerprint detection sensor is a type of fingerprint detection sensor detecting a fingerprint by measuring a difference in acoustic impedance between each valley and each ridge of the fingerprint by using an ultrasonic wave generation source, that is, a plurality of corresponding piezoelectric sensors, when the ultrasonic signals of a predetermined frequency discharged from the plurality of piezoelectric sensors are reflected from the valleys and ridges of the fingerprint. In particular, the ultrasonic type fingerprint detection sensor may be advantageous in that it has a function of detecting blood streams in fingers by generating pulse-type ultrasonic waves and detecting a Doppler effect due to the reverberation of the pulse-type ultrasonic waves, in addition to a function of simply detecting a fingerprint and thus, may determine whether the fingerprint has been forged by using the function.
Considering the fact that most blood stream flowing in the fingers are blood streams flowing along capillary vessels, very high intensity ultrasonic signals need to be generated to detect the blood stream by using the Doppler effect. To this end, the related art intentionally applies a phase delay to a plurality of ultrasonic signal generation units that generate and discharge the ultrasonic signals or applies a beam forming scheme thereto. However, in the case of the application of the phase delay or the beam forming scheme, circuit complexity, as well as an overall size are increased to degrade price competitiveness and cause problems in the miniaturization of fingerprint detection sensors, thereby leading to limitations in applicability.